A shape test for testing the external shape of a tire has generally been performed in a testing process performed after a tire curing step, which is the final step of a tire manufacturing process. The shape test is essential since tires are rubber products, and it is difficult to form tires in accurate shapes. In general, a visual and tactile test has been manually performed in the shape test. However, attempts have been made to automate the shape test by using a laser, a camera, etc, in recent years.
To automate the shape test of a tire, first, a sidewall section of the tire is irradiated with a linear light beam. An image of the linear light beam is captured with a camera, and a three-dimensional shape of the sidewall section is measured by the light-section method. When measuring the three-dimensional shape of the sidewall section, characters, logos, etc., included in the captured image of the sidewall section are detected through image processing, and the influence of normal projections and recesses that form the characters, logos, etc., is eliminated. Thus, the shape of the sidewall section including local irregularity defects and the like is determined.
In addition, with increase in width of a tread section, for example, technologies of shape test for the tread section have recently been developed, and a shape test for a region including a shoulder section, which is provided between the tread section and the sidewall section, has also been performed.
PTL 1 and PTL 2 disclose technologies for performing a shape test for the shoulder section.
According to PTL 1, a slit image of a tire crown section (shoulder section) is captured while imaging means and a tire are moved relative to each other, the imaging means including light emitting means that irradiates the tire crown section with slit light and image capturing means that captures an image of a section illuminated with the slit light. An RRO, which is a displacement of the circumferential shape of the tire from a central axis, is calculated by using shape data of the tire crown section. The shape data is calculated by using brightness data of the slit image, the brightness data reflecting projections and recesses in the tire crown section whose image has been captured.
PTL 2 discloses a tire shape detecting apparatus that captures an image of linear light with which a surface of a relatively rotating tire has been irradiated and that performs shape detection by the light-section method on the basis of the captured image to thereby detect a surface shape of the tire. The tire shape detecting apparatus includes linear light application means for emitting a plurality of linear light beams in a continuously joined manner so that a single light section line is formed on the surface of the tire, the linear light beams being emitted in directions different, from a detection height direction of the light section line; and image capturing means for capturing images of the plurality of linear light beams, with which the surface of the tire has been irradiated, in a direction in which the principal ray of each of the plurality of linear light beams is regularly reflected by the surface of the tire.